parse_url(url, partToExtract[, key]) - extracts a part from a URL
Parts: HOST, PATH, QUERY, REF, PROTOCOL, AUTHORITY, FILE, USERINFO
key specifies which query to extract
Example:
  > SELECT parse_url('http://facebook.com/path/p1.php?query=1', 'HOST') FROM src LIMIT 1;
  'facebook.com'
  > SELECT parse_url('http://facebook.com/path/p1.php?query=1', 'QUERY') FROM src LIMIT 1;
  'query=1'
  > SELECT parse_url('http://facebook.com/path/p1.php?query=1', 'QUERY', 'query') FROM src LIMIT 1;
  '1'